Nerve membranes are fluid bilayers in which specific mixtures of lipids and proteins form the excitation mechanism. This proposal is concerned with describing in a quantitative manner the physicochemical forces which control molecular mixing within membranes. The intra-membrane fluid environment is experimentally evaluated in the context of the thermodynamic principles of regular and ideal solutions. A novel planar bilayer composed of pure lipid (no solvent) is described. The bilayer represents the electrophysiological equivalent of the thermodynamic standard state in that it is composed of a single pure compound. The standard state membrane (SSM) can have a specific capacitance (greater than 950 nF/sq. cm) equal to that of nerve membranes. The membranes are ultra-thin (19A), large in area (1.3 sq. mm) and mechanically stable. Nonpolar anesthetics swell the bilayer by nearly 100%. The dielectric volume of the membrane is used as a sensitive indicator of concentration of anesthetics within the core of the fluid bilayer. The intra-membrane mixing energetics are considered in the context of solubility parameter theory and intra-membrane activity coefficients are measured. The mixing and de-mixing of different lipids (cholesterol, monoglyceride) are analyzed. Membrane lipid composition and conformation are related to the conduction and kinetics of polypeptide single channels. Destabilized ion channels are relatable to an anesthetic induced uncoiling of the bilayer lipid acyl chains.